The present invention relates to screen printing machines and more particularly to an improved printing head assembly and the machine resulting therefrom.
Heretofore, in screen printing machines for printing on fabric material, and particularly on articles of clothing, the printing head frames have been pivotally mounted at one end in a cantilevered arrangement with the framed-screen support carried in fixed position by the printing head frame. With an article to be printed supported on a pallet beneath a printing frame head, the latter was lowered from a raised position, like the lowering of a drawbridge, to position the screen down upon the article in question. Then flood and squeegee blades were operated to accomplish a flooding stroke followed by a squeegee stroke. Thereafter the entire printing head was raised to free the underlying article and pallet.
A typical example of a printing head construction as outlined above is described in U.S. Pat. No. 3,885,493 issued May 27, 1975 to Precision Screen Machines, Inc. on an application by David Jaffa. In another Jaffa patent, U.S. Pat. No. Re. 29,160, reissued Mar. 29, 1977 and entitled "Screen Printing Machine With Oval Rail For Indexing Pallets", there is described a screen printing machine having an oval track or rail about which a series of pallets supporting a workpiece are indexed from station to station. The arrangement is such that the pallets travelling about the oval rail are always disposed or maintained in a common plane. A printing head assembly having one or more color stations, is operatively associated for movement into and out of printing relationship with one or more of the pallets as the pallets are indexed and maintained in a common plane.
As a variant on the oval track arrangement, machines have been built where the pallets are arranged at the ends of radial arms extending from a central vertical shaft and index around a circular path as the shaft rotates. Both the oval track and circular path machines were constructed with hinged cantilever printing heads. Each such printing head represented a large physical mass which, during machine operation, caused noticeable and often objectionable machine vibration. Also, large motive devices or actuators were required to move the printing heads, and a massive machine structure was required to produce an apparatus capable of operating at acceptable production speed.
Therefore, it is an object of the present invention to provide a screen printing machine capable of operating at higher speed than presently known machines. It is a further object to provide such machine operation with a concomitant reduction in vibration. It is also an object to provide for economy of operating power while obtaining equal or better throughput than heretofore obtainable with known machines.